Our invention relates to vehicle headlamps, particularly to those having a dual filament bulb for emitting both an upper beam for distant illumination and a lower beam for illumination of the road ahead of the vehicle when meeting or following another vehicle. More particularly, our invention deals with improvements concerning a bulb shade in such a dual beam vehicle headlamp.
Reflectors shaped like a paraboloid of revolution have been used extensively in vehicle headlamps. In headlamps that are elongated horizontally, primarily for aesthetic purposes, the paraboloidal reflectors have been modified in shape to include flat top and bottom portions in conformity with the shape of the headlamp. Such modified paraboloidal reflectors have given rise to a problem in connection with the flat top portion.
Should the flat top portion of the modified paraboloidal reflector be irradiated directly by a light source such as a dual filament bulb, the headlamp would emit rays of light that were angled sharply downwardly of the vehicle. Some of such light rays would then be reflected again by the front bumper of the vehicle thereby to be diffusely directed upwardly. Such diffuse upward rays would be particularly objectionable during a rainfall as they would produce a glaring screen of light by irradiating the raindrops. Such a glaring light screen would, of course, represent a serious hazard to traffic safety.
We know that a bulb shade has conventionally been employed to prevent the bulb from directly irradiating the flat top portion of the modified paraboloidal reflector. The conventional bulb shade has generally extended parallel to the optical axis of the headlamp. This conventional arrangement of the bulb shade has presented an inconvenience when it has been employed in combination with a dual filament bulb to provide a vehicle headlamp capable of emitting an upper and a lower beam.
As is well known to those versed in the motor vehicle lighting art, the dual filament bulb for use in the dual beam headlamp has a primary and an auxiliary filament contained in a single envelope of vitreous material. Disposed at the focus of the paraboloidal reflector, the primary filament provides the upper beam. The auxiliary filament is displaced from the primary filament in a direction away from the reflector. The light rays that have been emitted by the auxiliary filament become convergent on being reflected by the paraboloidal reflector. The lower beam, which must be angled downwardly, is therefore obtainable by those of the light rays that have been emitted by the auxiliary filament which have been reflected by the upper half of the paraboloidal reflector.
However, as mentioned above, the bulb shade has so far been disposed between the bulb and the flat top portion of the paraboloidal reflector and parallel to the optical axis. So disposed, the conventional bulb shade has cut off some of the light rays that have been emitted by the auxiliary filament and that have been reflected by the upper half of the paraboloidal reflector to provide the lower beam.
It should be borne in mind that, even without the bulb shade, the lower beam is provided only by those of the light rays that have been emitted by the auxiliary filament which have been reflected by the upper half of the paraboloidal reflector. It will be apparent, then, that a further reduction of the amount of such light rays by the conventionally disposed bulb shade represents a serious waste of energy.